1. Field of the Invention
The present invention relates to a sputtering target having a target material joined onto an outer peripheral surface of a cylindrical backing member, and a method for manufacturing the same.
2. Prior Art
Conventional sputtering targets extensively in use are of a planer type having a circular or square plate-like shape. However, the targets of this type have the disadvantages that the amount of consumable target material is only about 30 to 40%, and that a continuous sputtering operation or sputtering onto an elongated substrate cannot be carried out. Therefore, targets of a cylindrical shape have recently come into use.
For manufacturing cylindrical targets, the following various methods are known:
(A) Plasma flame coating method:
This method involves flame-coating a target material on the outer peripheral surface of a backing tube using plasma jet generated in an atmosphere of an inert gas or in ambient air, to thereby produce a target of a cylindrical shape. This method has been applied in the manufacture of targets of Si (silicon), Cr (chromium), Sn (stannum or tin) or the like.
(B) Casting (Fusion) method:
This method involves forming a tubular mold around the periphery of a backing tube, and introducing a molten target material into the space between the backing tube and the mold, to thereby manufacture a cylindrical target. This method can be employed for manufacturing targets of metals having low melting points, e.g., Zn (zinc) or Sn.
(C) Flame coating method:
This method involves flame-coating a fused target material on the outer peripheral surface of a backing tube, using high pressure gas, to thereby manufacture a cylindrical target. This method may also be applied to the targets of metals with low melting points, such as Zn or Sn.
(D) Electroplating method:
This method involves immersing a backing tube in an electroplating bath so as to serve as a cathode, and depositing metal ions in the electrolyte, on the outer peripheral surface of the backing tube, to thereby manufacture a cylindrical target. This method is applied to the targets of Cr, Sn or the like.
The above various methods, however, have the following disadvantages:
In the plasma flame coating method, gas is easily occluded in the target, and the gas causes defects therein. Therefore, the resulting target comes to have a low density. In addition, a reaction layer may be formed between the target material and the backing tube.
Furthermore, the casting method has the disadvantages that its application is limited only to the metals with low melting points such as Zn, Sn or the like, and that the resulting target is susceptible to casting defects.
On the other hand, in the flame coating method, the temperature of the melt can be controlled so as to be constant, and therefore targets with less defects can be obtained. However, this method is still only applicable to the metals with low-melting points, and a large-scale facility is required, so that the manufacturing costs of targets are unduly increased.
Moreover, in the electroplating method, although the target material strongly adheres to the backing tube, it takes a prolonged period of time for metal ions to be deposited, and the thicknesses of the resulting targets are limited.
As described above, the known methods have various disadvantages. Therefore, cylindrical targets of Cr, Mo (molybdenum) or the like manufactured by a powder molding method have been employed in practice.
FIG. 3 depicts an example of such a cylindrical target 1 manufactured by the conventional powder molding method. This target 1 includes a cylindrical target material 2 and a backing tube 4 of stainless steel inserted into a hollow portion 3 thereof, and solder material 5 is filled into the space between the target material 2 and the backing tube 4 to join them together. The target of this construction is consumed at a high ratio of 80 to 90%, and a glass surface or a mirror surface can be sputtered uniformly over its wide area using this target. Therefore, the field of application of this type of target would be widened in the future.
This cylindrical target 1 is usually manufactured according to the following method.
First, a material powder for targets is introduced into a cylindrical stainless steel can (mold), which is then sealed. Subsequently, hot isostatic pressing is carried out to provide a cylindrical sintered body 11 (see FIG. 4(a)), and the resulting sintered body 11 is machined into a cylindrical target material 2 (see FIG. 4(b)). Thereafter, the solder material 5 is filled into the space between the target material 2 and the backing tube 4 to join them together (see FIG. 4(c)).
In the aforesaid method for manufacturing the target 1, since the sintered body 11 is machined into a cylindrical shape, it is very difficult to work its inner surface, resulting in a large loss of material. Furthermore, inasmuch as the method involves the steps of inserting the backing tube 4 into the hollow portion 3 of the target material 2, and filling the space between the target material 2 and the backing tube 4 with the solder material 5, it is very difficult to align the backing tube 4 with the target material 2, and additionally high precision must be attained with respect to diameters of these members. Furthermore, since the target material 2 and the backing tube 4 are joined together through the solder material 5, bonding strength is weak.